1. Field of the Invention
The present invention relates to a protecting mechanism for a laser scanner unit for effecting exposure of a photosensitive body in a laser printer.
2. Description of Related Art
As described in U.S. Pat. No. 4,588,280, a known laser printer is generally constructed such that it can be divided into an upper body and a lower body with a paper transport path defined as a boundary therebetween for convenience of easy clearance of a paper jam. In such a laser printer, the upper body includes a laser scanner unit that precisely directs the path of a laser beam onto a photosensitive body. Further, an integral process cartridge, or an assembly of components, including an image forming means comprising a photosensitive body, developer, cleaner and corona discharger is also mounted in the upper body.
Although these elements of the image forming means are normally exchanged as consumables by a service engineer, the use of a process cartridge enables the operator or user to easily exchange the photosensitive body, developer, cleaner containing spent toner, and corona discharger.
However, in the above conventional laser printer using the process cartridge, the process cartridge is exchanged with the upper body open. Accordingly, when the process cartridge is removed from the upper body, the exposure opening of the laser scanner unit is exposed to the environment. If such an exposed condition of the exposure opening inadvertently lasts too long, there is a strong possibility, practically a certainty, that dust or other solid particles will enter the laser scanner unit from the exposure opening and be deposited on a lens or a mirror that are components of the laser scanner unit. The result is a degradation in the quality of the image formed.
Further, the correcting optical system for the laser beam, e.g., a cylindrical lens is located in the vicinity of the exposure opening of the laser scanner unit. In this type laser printer, when the upper body is opened, and the process cartridge is removed from the upper body for exchange, the operator can easily touch the cylindrical lens with his hand causing a stain on or mark the surface of the lens. As a result, the exposure of the photosensitive body by the laser beam is adversely effected which also greatly reduces image quality.